To
implement this first we need to get Ionic.Zip.dll from DotnetZIP
Library for that check this link Ionic.Zip.dll or you can get it
from attached downloadable code. Now you need to add that dll to your
application bin folder for that
check below steps

Go
to Solution Explorer -à Right click on it and go to Add
ASP.NET folder -à click on Bin

Now
bin folder added to our application and place Ionic.Zip.dll in that folder and
add another folder in your application (Right click on your application -à Select New folder)
and give name as SampleFiles

Once
you added dll and SampleFiles folder
our application will be like this

Now
write the following code to upload files and download selected files as zip
folder from gridview